This application is based upon and claims priority of Korean Patent Application No. 98-41503 filed Oct. 2, 1998, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical pickup of an optical disk drive for recording and/or reproducing information on/from an optical disk. More particularly, the present invention relates to an optical pickup for an optical disk drive, the optical pickup having a light path controlling device to control occurrence of beam shift and field angle.
2. Description of the Related Art
A conventional optical disk drive projects a laser beam to an information recording surface of an optical disk, detects a signal based on the reflectivity, the phase, the polarized light variation and the like of the laser beam reflected from the information recording surface, and processes the signal thereby obtaining required information recorded on the information recording surface.
As shown in FIG. 1, the conventional optical disk drive includes an optical pickup 1 for projecting the laser beam to an optical disk 40 and for detecting the signal from the reflected laser beam, a driving section 2 for moving the optical pickup 1 to a predetermined position with respect to the information recording surface of the optical disk 40, a signal processing section 3 for processing the signal detected by the optical pickup 1 to convert the signal into the required information, and a controlling section 4 for controlling the above elements. The driving section 2 includes a spindle motor 5 for rotating the optical disk 40, a thread motor 6 for moving the optical pickup 1, and a servo section 7 for controlling the spindle motor 5 and thread motor 6.
When an external signal is input to the conventional optical disk drive shown in FIG. 1 and described above, the optical pickup 1 is moved in a radial direction of the optical disk 40 by the operation of the driving section 2, while recording information to the optical disk 40 and detecting the signals recorded in the information recording surface of the optical disk 40 by projecting the laser beam to the optical disk 40. The detected signals are processed by the signal processing section 3, converted into the required information, and then output to external devices.
In the above-described conventional optical disk drive, the optical pickup 1 is an essential element for recording information to and detecting information from the information recording surface of the optical disk 40. The optical pickup 1 includes a laser beam source for generating the laser beam, an optical system for projecting the laser beam generated from the laser beam source to the information recording surface of the optical disk 40, and a pickup base for fixedly supporting the laser beam source and the optical system. A laser diode is utilized as the laser beam source, and the optical system includes a collimating lens, a reflective mirror, and an objective lens.
However, an error with respect to a light emitting point and a light emitting angle may occur in the process of manufacturing the conventional optical pickup 1. Further, an error may occur in parts of the optical system during the process of manufacturing or assembling. One type of error, referred to hereinafter as xe2x80x9cbeam shiftxe2x80x9d, occurs when the central line of an objective lens does not coincide with the central line of a collimating lens, resulting in the central line of the laser beam source not coinciding with the collimating lens. Another type of error, referred to hereinafter as xe2x80x9cfield anglexe2x80x9d, occurs when the central line of the laser beam does not coincide with the center of the collimating lens, causing the central line of the laser beam to be received by the objective lens in a non-perpendicular relation thereto. The combination of errors bring an asymmetric distribution of the laser beam intensity. The beam shift and/or field angle should be controlled within a predetermined range, since these two errors cause malfunctions in recording and/or reproducing the information with respect to the information recording surface of the optical disk 40. Accordingly, the optical pickup 1 usually includes light path controlling means for controlling the possible occurrence of the beam shift and field angle.
The optical pickup 1 of the conventional optical disk drive will be described in more detail hereinafter with respect to FIG. 2, which is a schematic diagram of the optical pickup 1. As shown in FIG. 2, the optical pickup 1 includes an objective lens 11 disposed at an upper-side surface of a pickup base 10, and a reflective mirror 12 disposed below the objective lens 11 to reflect the laser beam projected by the objective lens 11 through a light path. Further, a collimating lens 13 and a laser diode 14 are arranged in sequential order in the light path.
The laser beam generated from the laser diode 14 is transmitted through the collimating lens 13 and projected to the reflective mirror 12, where the laser beam is reflected to the objective lens 11 to be projected to the information recording surface of the optical disk 40 which is positioned thereabove.
The collimating lens 13 is supported within a first light path adjusting plate 20, while the laser diode 14 is supported within a second light path adjusting plate 30. The first light path adjusting plate 20 is movably disposed at the end portion of the pickup base 10 so as to move upward/downward and leftward/rightward with respect to the pickup base 10. Further, the second light path adjusting plate 30 is movably disposed at the end portion of the first light path adjusting plate 20 so as to be moved in vertical and lateral directions with respect to the collimating lens 13. When the first light path adjusting plate 20 is moved, the second light path adjusting plate 30 is also moved together therewith. However, the movement of the second light path adjusting plate 30 does not affect the movement of the first light path adjusting plate 20.
The beam shift and field angle can be adjusted by moving the first and second light path adjusting plates 20 and 30. The adjustment of the beam shift and field angle with the conventional optical pickup 1 will be described hereinafter with reference to FIGS. 3A through 3D.
FIGS. 3A through 3D are views illustrating the light path controlling operation of the conventional optical pickup 1. For the purpose of convenience in description, the laser diode 14, the collimating lens 13, the objective lens 11, and the optical disk 40 are arranged in a straight line in the figures while the reflective mirror 12 is omitted.
FIG. 3A illustrates the situation in which a beam shift has occurred. As shown in FIG. 3A, in the situation in which a beam shift has occurred, the laser beam generated from the laser diode 14 coincides with a central line of the collimating lens 13, while the objective lens 11 is not aligned with the collimating lens 13 so that the central line A of the laser beam is upwardly deviated toward the objective lens 11. Accordingly, the laser beam has an unbalanced light intensity distribution on the optical disk 40. The portions shown by the dotted lines in FIG. 3A are where the light intensity distribution is balanced.
The beam shift shown in FIG. 3A can be adjusted by moving the first light path adjusting plate 20 downward such that the central line A of the laser beam coincides with the center of the objective lens 11, as shown in FIG. 3B. Since the second light path adjusting plate 30 is moved along with the first light path adjusting plate 20, the beam shift can be adjusted without affecting the field angle.
FIG. 3C illustrates a situation in which the field angle has occurred, and FIG. 3D illustrates adjustment of the field angle.
As shown in FIG. 3C, the objective lens 11 and the collimating lens 13 are precisely aligned with each other, while the central line B of the laser beam generated from the laser diode 14 is deviated downward as a result of the non-coincidence of the laser beam with the center of the collimating lens 13. In a situation in which the field angle has occurred, the field angle may be adjusted by moving the second light path adjusting plate 30 upward such that the center of the laser beam coincides with the center of the collimating lens 13, as shown in FIG. 3D.
As described above, the beam shift and the field angle can be adjusted by moving the first and second light path adjusting plates 20 and 30 vertically and laterally. However, since the conventional optical pickup 1 described above is constructed to adjust the beam shift and the field angle by moving the first and second light path adjusting plates 20 and 30 vertically and laterally, a space is required for permitting the movement of the first and second light path adjusting plates 20 and 30. As a result of the space to permit movement of the first and second light path adjusting plates 20 and 30, a problem arises in that the size of the conventional optical pickup is increased.
Further, since the collimating lens 13 of the conventional optical pickup is supported by the first light path adjusting plate 20, the size of first light path adjusting plate 20 is enlarged when lengthening the focal distance of the collimating lens 13. Moreover, since the movement range of the collimating lens 13 becomes wide in proportion to the focal distance of the collimating lens 13, the size of the optical pickup inevitably becomes larger.
It is an object of the present invention to overcome the above-described problems of the prior art, and to provide an optical pickup of an optical disk drive to precisely adjust a beam shift and a field angle, without increasing the size of the optical pickup, by moving and/or rotating a light emitting point of a laser beam source with respect to a collimating lens to control the light path with respect to the beam shift and the field angle.
Another object of the present invention is to provide an optical pickup for an optical disk drive which is not increased in size, regardless of the focal distance of the collimating lens, even when a focal distance of a collimating lens is increased as a result of a controlling operation of the light path with respect to a beam shift and a field angle.
Objects and advantages of the present invention are achieved in accordance with embodiments of the present invention with an optical pickup of an optical disk drive comprising a laser beam source to generate a laser beam; a pickup base including an objective lens to project the laser beam generated from the laser beam source to an information recording surface of an optical disk; and a light path controlling device, disposed on the pickup base, to support the laser beam source, and to control a light path of the laser beam with respect to a field angle and a beam shift by at least one of moving and rotating the light emitting point of the laser beam source with respect to an optical axis of the objective lens.
The optical pickup may further comprise a collimating lens to convert the laser beam generated from the laser beam source into a parallel ray, and a reflective mirror to reflect the laser beam transmitted through the collimating lens to the objective lens, wherein the collimating lens and the reflective mirror are respectively fixed to the pickup base.
In accordance with the present invention, the light path controlling device comprises a variation adjusting plate disposed on the pickup base and movable in vertical and lateral directions, the variation adjusting plate including and a rotational hole formed in a central portion thereof; and a rotation adjusting plate including a rotational section having a predetermined curvature and a laser beam source fixed to the rotation adjusting plate, the rotational section being inserted into the rotational hole of the variation adjusting plate and rotatable with respect to the variation adjusting plate, wherein the field angle is adjusted by moving the variation adjusting plate in the vertical and lateral directions, and the beam shift is adjusted by rotating the rotation adjusting plate.
The rotational hole and the rotational section may be formed into hemispherical shapes which correspond to each other so that the rotational section is rotated while contacting the rotational hole.
The rotational hole may be formed into a circular shape, and the rotational section may be formed into a hemispherical shape, so that the rotational section is rotated while contacting the circular rotational hole.
In accordance with the present invention, the pickup base includes a plurality of screw fitting holes formed around an opening in the pickup base, the variation adjusting plate includes a plurality of screw passing holes aligned with the screw fitting holes, and the variation adjusting plate is fixed to the pickup base by a plurality of bolts which are inserted into the plurality of screw fitting holes after being passed through the screw passing holes, wherein the respective diameters of the plurality of screw passing holes in the variation adjusting plate are larger than the respective diameters of each bolt, wherein the variation adjusting plate is moved in the vertical and lateral directions to a proper position, and then fixed in the proper position.
In accordance with embodiments of the present invention, the variation adjusting plate includes an upper side, a lower side, a right side and a left side, and the rotation adjusting plate is fixed to the variation adjusting plate by one of the upper and lower sides and by one of right and left sides with an elastic member, and two sides of the variation adjusting plate which are not fastened by the elastic member are fastened by respective adjusting screws, wherein the rotation adjusting plate is rotated when the respective adjusting screws are rotated.
In accordance with the present invention, one end of the elastic member contacts the rotation adjusting plate, while another end of the elastic member is aligned with a screw passing hole of the variation adjusting plate, and is fastened to the variation adjusting plate by a bolt passed through the screw passing hole, wherein the elastic member elastically supports the rotation adjusting plate.
Objects and advantages of the present invention are achieved in accordance with preferred embodiments of the present invention, with an optical pickup of an optical disk drive comprising a laser beam source to generate a laser beam; an optical system including a collimating lens to convert the laser beam generated from the laser beam source into a parallel ray, a reflective mirror to reflect the parallel laser beam converted by the collimating lens in a vertical direction, and an objective lens to project the laser beam reflected from the reflective mirror to an information recording surface of an optical disk; a pickup base to fixedly support the collimating lens, the reflective lens, and the objective lens of the optical system; a variation adjusting plate disposed on the pickup base and movable in vertical and lateral directions, the variation adjusting plate having a rotational hole formed in a central portion of the variation adjusting plate, and a rotation adjusting plate including a rotational section having a predetermined curvature inserted into the rotational hole of the variation adjusting plate, and the laser beam source fixed therein, the rotation adjusting plate being rotated with respect to the variation adjusting plate, wherein a light path with respect to a field angle and a beam shift is controlled by at least one of moving and rotating a light emitting point of the laser beam source with respect to an optical axis of the collimating lens.
In accordance with the present invention, since the collimating lens is fixed to the pickup base, which is a separate structure with respect to the light path controlling device, and since a light path with respect to a field angle and a beam shift is controlled by moving and/or rotating a light emitting point of the laser beam source with respect to an optical axis of the collimating lens, less space is required for the movement of the light path controlling device, and the size of the optical pickup becomes smaller.
Further, in accordance with the present invention, since the collimating lens is fixed to the pickup base, which is the separate structure with respect to the light path controlling device, the light path with respect to the field angle and the beam shift can be controlled regardless of the focal distance of the collimating lens. Accordingly, even when the focal distance of the collimating lens is lengthened, the beam shift and the field angle can be precisely adjusted without increasing the size of the optical pickup.